Synthesis of high activity ZSM-48

ABSTRACT

A process for producing ZSM-48 comprises crystallizing an aqueous reaction mixture comprising at least one source of silica, at least one source of alumina, at least one source of hydroxyl ions, at least one source of diquaternary alkylammonium, R 2+ , ions having the formula:
 
(CH 3 ) 3 N + (CH 2 ) 5 N + (CH 3 ) 3  
 
and optionally ZSM-48 seed crystals, wherein said reaction mixture has a composition including the following molar ratios:
 
     
       
         
               
               
               
             
                   
                   
               
                   
                 R 2+ :SiO 2   
                 less than 0.1 
               
                   
                 SiO 2 :Al 2 O 3   
                 less than 100 
               
                   
                 OH − :SiO 2   
                 less than 0.2.

FIELD

This invention relates to the synthesis of high activity ZSM-48 and itsuse as a catalyst, especially in the dewaxing of hydrocarbon feedstocks.

BACKGROUND

ZSM-48 is a zeolite with orthorhombic or pseudo-orthorhombic symmetryhaving ten-ring non-interconnecting, linear channels whose idealdimensions are 5.5×5.6 Å. ZSM-48 has shown attractive properties as acatalyst for the dewaxing of hydrocarbon feedstocks, see for exampleU.S. Pat. Nos. 5,075,269 and 6,884,339 and International Publication WO01/64339. As a result, there is considerable interest in finding newmethods of synthesizing ZSM-48 and, in particular, ZSM-48 with high acidactivity (that is, low silica/alumina molar ratio).

ZSM-48 was first synthesized by Rollmann et al. using a C₄ to C₁₂organic diamine as a structure-directing agent, see U.S. Pat. No.4,423,021. As synthesized by Rollman et al., the zeolite containedlittle or no aluminum and so had little acid activity.

Synthesis of ZSM-48, again with a high silica to alumina molar ratio, inthe presence of a mixture of a C₂ to C₁₂ alkylamine and a C₃ to C₅tetramethylammonium compound is described in U.S. Pat. No. 4,397,827 andin the presence of bis(N-methylpyridyl)ethylinium cations in U.S. Pat.No. 4,585,747.

U.S. Pat. No. 5,961,951 discloses synthesis of ZSM-48 in the presence ofethylene diamine as the structure-directing agent. However, the broaddefinition of the reaction mixture requires a silica/alumina molar ratioof at least 100 and the only example for which the composition of theZSM-48 product is cited, Example 2, reports the silica/alumina molarratio as being 170.

European Patent Publication EP-A-142317 discloses synthesis of ZSM-48 inthe presence of certain linear diquaternary compounds having the generalformula:[(R′)₃N⁺(Z)_(m)[(R′)₃N⁺](X⁻)₂in which each R′ is an alkyl or heteroalkyl group having from 1 to 20carbon atoms, a cycloalkyl or cycloheteroalkyl group having from 3 to 6carbon atoms or an aryl or heteroaryl group; Z is an alkylene orheteroalkylene group having from 1 to 20 carbon atoms, an alkenylene orheteroalkenylene group having from 2 to 20 carbon atoms or an arylene orheteroarylene group; m is 5, 6, 8, 9 or 10 and X⁻ is an anion.EP-A-142317 reports that the silica/alumina molar ratio of the reactionmixture must be at least 100 since at lower values a different silicateframework is produced.

U.S. Pat. No. 6,923,949 discloses pure phase ZSM-48 crystals having aXO₂/Y₂O₃ ratio of less than about 150/1, where X is at least one of Sior Ge, preferably Si, and Y is at least one of Al, Ga, B, Fe, Ti, V andZr, preferably Al, and free from ZSM-50 and Kenyaite impurities having adiameter of less than about 1 micron and being substantially free offibrous morphology. The material is produced by crystallizing a reactionmixture comprising at least one organic template material selected fromorganic linear diquaternary alkyl ammonium compounds and linear diaminoalkanes, and heterostructural zeolite seeds selected from ZSM-5, ZSM-11,ZSM-12, colloidal BEA, Beta, X and Y zeolites. The Examples employhexamethonium chloride as the linear diquaternary alkyl ammoniumcompound and produce ZSM-48 crystals with a SiO₂/Al₂O₃ molar ratio aslow as 67.7.

International Publication No. WO 2007/070521 discloses synthesis of acomposition comprising ZSM-48 crystals having a silica:alumina molarratio of 110 or less that is free of non ZSM-48 crystals and free ofZSM-50 by crystallizing a reaction mixture comprising an aqueous mixtureof silica or silicate salt, alumina or aluminate salt, hexamethoniumsalt and alkali base wherein the reaction mixture has the followingmolar ratios: silica:alumina molar ratio from 70 to 110, base:silicafrom 0.1 to 0.3 and hexamethonium salt:silica from 0.01 to 0.05.Production of ZSM-48 crystals with a silica:alumina molar ratio as lowas 80 are exemplified.

In an article entitled “Reinvestigation into the synthesis of zeolitesusing diquaternary alkylammonium ions (CH₃)₃N⁺(CH₂)_(n)N⁺(CH₃)₃ withn=3−10 as structure-directing agents”, Microporous and MesoporousMaterials, 68 (2004), 97-104, Song-Ho Lee et al. describe the effects ofsynthesis variables, especially, the type and concentration of alkalications on the phase selectivity of zeolite crystallization in thepresence of Me₆-diquat-n ions where n varies between 3 and 10. Inparticular, Song-Ho Lee et al. report in Table 2 that with a synthesismixture containing Me₆-diquat-5 and having an silica/alumina molar ratioof 60 and a diquat/silica molar ratio of 0.1, crystallization producesZSM-48 when the OH⁻/SiO₂ molar ratio of the mixture is 0.33 or less butproduces ZSM-12 at an OH⁻/SiO₂ molar ratio of 0.47 and MCM-22 atOH⁻/SiO₂ molar ratios of 0.6 and 0.73. At even higher OH⁻/SiO₂ molarratios, the product is mordenite and/or analcime.

According to the invention, it has now been found that, in the synthesisof high activity ZSM-48 using Me₆-diquat-5 as a structure-directingagent, the diquat/silica molar ratio is a critical variable impactingthe phase selectivity of the product. Moreover, it has been found thatby using a combination of Me₆-diquat-5 and Me₆-diquat-6 as thestructure-directing agent, it is possible to exercise control over themorphology of the resultant ZSM-48 crystals.

SUMMARY

In one aspect, the present invention resides in a process for producingZSM-48, the process comprising:

(a) providing an aqueous reaction mixture comprising at least one sourceof silica, at least one source of alumina, at least one source ofhydroxyl ions, at least one source of diquaternary alkylammonium, R²⁺,ions having the formula:(CH₃)₃N⁺(CH₂)₅N⁺(CH₃)₃and optionally seed crystals, wherein said reaction mixture has acomposition including the following molar ratios:

R²⁺:SiO₂ less than 0.1 SiO₂:Al₂O₃ less than 100 OH⁻:SiO₂ less than 0.2;and

(b) crystallizing said reaction mixture under conditions effective toproduce said ZSM-48.

Conveniently, said reaction mixture has a composition including thefollowing molar ratios:

R²⁺:SiO₂ from about 0.01 to about 0.05 SiO₂:Al₂O₃ from about 50 to lessthan 100 OH⁻:SiO₂ from about 0.1 to about 0.2.

Conveniently, said reaction mixture has an H₂O:SiO₂ molar ratio lessthan 30 and in one embodiment also comprises a source of sodium cations,typically such that the mixture has a Na⁺:SiO₂ molar ratio less than0.2.

Conveniently, said reaction mixture also comprises a source of furtherdiquaternary alkylammonium ions having the formula(CH₃)₃N⁺(CH₂)_(n)N⁺(CH₃)₃ where n is 3, 4, 6, 7, 8, 9 or 10 andespecially where n is 6.

In a further aspect, the present invention resides in a process forproducing ZSM-48, the process comprising crystallizing an aqueousreaction mixture comprising at least one source of silica, at least onesource of alumina, at least one source of hydroxyl ions, at least onesource of first diquaternary alkylammonium ions having the formula:(CH₃)₃N⁺(CH₂)₅N⁺(CH₃)₃at least one source of second diquaternary alkylammonium ions having theformula:(CH₃)₃N⁺(CH₂)_(n)N⁺(CH₃)₃where n is 3, 4, 6, 7, 8, 9 or 10 and especially is 6, andoptionally, seed crystals.

Conveniently, said reaction mixture has a SiO₂:Al₂O₃ molar ratio lessthan 100.

Conveniently, the molar ratio of total diquaternary alkylammonium ionsto SiO₂ in the reaction mixture is less than 0.1.

In all of the above embodiments, the reaction mixture preferablycomprises seed crystals, more preferably ZSM-48 seed crystals.Conveniently, the ZSM-48 seed crystals are present in an amount betweenabout 50 ppm by weight to about 50,000 ppm by weight of the reactionmixture.

Conveniently, the crystallizing conditions include a temperature ofabout 120° C. to about 200° C. for a time of about 12 to about 200hours.

In yet a further aspect, the present invention resides in a method fordewaxing a hydrocarbon feedstock, comprising contacting the hydrocarbonfeedstock under dewaxing conditions with ZSM-48 prepared by the processdescribed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an X-ray diffraction pattern of the as-synthesized product ofExample 1.

FIG. 1B is a scanning electron micrograph (SEM) of the as-synthesizedproduct of Example 1.

FIG. 2A is an X-ray diffraction pattern of the as-synthesized product ofExample 2.

FIG. 2B is a scanning electron micrograph (SEM) of the as-synthesizedproduct of Example 2.

FIG. 3A is an X-ray diffraction pattern of the as-synthesized product ofExample 4.

FIG. 3B is a scanning electron micrograph (SEM) of the as-synthesizedproduct of Example 4.

FIG. 4A is an X-ray diffraction pattern of the as-synthesized product ofExample 5.

FIG. 4B is a scanning electron micrograph (SEM) of the as-synthesizedproduct of Example 5.

FIG. 5A is an X-ray diffraction pattern of the as-synthesized product ofExample 6.

FIG. 5B is a scanning electron micrograph (SEM) of the as-synthesizedproduct of Example 6.

FIG. 6A is a graph of n-decane conversion against temperature in then-decane isomerization process of Example 8.

FIG. 6B is a graph of iso-decane yield against n-decane conversion inthe n-decane isomerization process of Example 8.

DETAILED DESCRIPTION

The present invention is directed to a process for producing ZSM-48,especially high activity ZSM-48 having a silica to alumina molar ratioless than 100, and to the use of the resultant ZSM-48 as a catalyst indewaxing hydrocarbon feedstocks.

In the present process, ZSM-48 is produced by crystallizing an aqueousreaction mixture comprising at least one source of silica, at least onesource of alumina, at least one source of hydroxyl ions, a directingagent comprising at least one source of Me₆-diquat-5 ions, also referredto herein as pentamethonium ions, which are diquaternary alkylammoniumions having the formula:(CH₃)₃N⁺(CH₂)₅N⁺(CH₃)₃,and optionally seed crystals, wherein the aqueous reaction mixture has acomposition including the following molar ratios:

R²⁺:SiO₂ less than 0.1, such as from about 0.01 to about 0.05 SiO₂:Al₂O₃less than 100, such as from about 50 to less than 100, and OH⁻:SiO₂ lessthan 0.2, such as from about 0.1 to about 0.2.

Generally, the reaction mixture also has an H₂O:SiO₂ molar ratio lessthan 30, or even less than 20, so that higher yields of the desiredZSM-48 product can be produced. In one embodiment, the reaction mixturealso comprises a source of sodium cations, typically such that thereaction mixture has a Na⁺:SiO₂ molar ratio less than 0.2. A suitablesource of sodium ions is sodium hydroxide, which of course also providesa suitable source of hydroxyl ions.

The reaction mixture preferably contains seed crystals, typicallyzeolite seed crystals of a different or identical framework type asZSM-48. More preferred seed crystals are ZSM-48 seed crystals. If used,the ZSM-48 seed crystals are generally added to the aqueous reactionmixture so as to be present in an amount between about 50 ppm by weightto about 50,000 ppm by weight. In general, at least 100 ppm by weight ofseed crystal is employed, preferably 100 ppm to 5000 ppm by weight, morepreferably 500 ppm to 3000 ppm by weight, of the reaction mixture. Inone embodiment, the ZSM-48 selected for use as the seed crystals has asilica to alumina molar ratio less than 100.

Any reactive form of silica can be employed as a source of silica in thepresent reaction mixture, with suitable commercially available materialsbeing fumed silica, precipitated silica, silica gels, silicic acid, atetraalkyl orthosilicate, or an aqueous colloidal suspension of silica.In general, fumed silica appears to assist in producing ZSM-48 with alow silica to alumina molar ratio and high purity.

Similarly, any reactive form of alumina can be employed as an aluminasource, although generally water soluble sources of alumina such as analuminate or an aluminum salt, such as aluminum nitrate, are preferred.Other suitable sources of alumina include hydrated alumina, such asgamma-alumina, pseudobohemite and colloidal alumina.

The source of Me₆-diquat-5 ions in the reaction mixture can be anyreadily available pentamethonium salt, such as a dihalide, especially adichloride or dibromide, or pentamethonium dihydroxide.

Although the present synthesis process can be employed with Me₆-diquat-5ions as the only structure directing agent, in some embodiments it maybe desirable to employ a mixture of Me₆-diquat-5 ions with at least onedifferent diquaternary ammonium compound as the structure directingagent. In this case, the different diquaternary ammonium compound hasthe formula:(CH₃)₃N⁺(CH₂)_(n)N⁺(CH₃)₃where n is 3, 4, 6, 7, 8, 9 or 10 and especially is 6. The Me₆-diquat-6cation is also referred to herein as the hexamethonium cation. Thus, itis found that by using such a mixture of diquaternary ammoniumcompounds, and in particular a mixture of Me₆-diquat-5 ions andMe₆-diquat-6 ions, it may be possible to produce ZSM-48 with a lowersilica to alumina molar ratio and/or a different morphology that isobtainable with either diquat alone. For example, although Me₆-diquat-5alone appears to favor the formation of ZSM-48 with needle- orfibrous-like morphology, a mixture Me₆-diquat-5 ions and Me₆-diquat-6ions seems to favor crystals with a lower length to diameter ratio.

Where a mixture of Me₆-diquat-5 ions with at least one differentdiquaternary ammonium compound is employed as the structure directingagent, the molar ratio of the Me₆-diquat-5 ions to said at least onedifferent diquaternary ammonium compound is generally such thatMe₆-diquat-5 ions represent 10% to 90% of the total diquaternaryalkylammonium ions. Moreover, the total amount of the Me₆-diquat-5 ionsand said at least one different diquaternary ammonium compound presentin the reaction is generally arranged so that the molar ratio of totaldiquaternary alkylammonium ions to SiO₂ is less than 0.1.

The crystallization conditions used in the present process are notclosely controlled but in general include a temperature of about 120° C.to about 200° C., such as about 140° C. to about 180° C., for a time ofabout 12 to about 200 hours, such as about 20 to about 120 hours.Crystallization can be carried out at either static or, preferably,stirred conditions in a suitable reactor vessel, such as for example,polypropylene jars or Teflon™-lined or stainless steel autoclaves. Whencrystallization is complete, the ZSM-48 product is separated from themother liquor, typically by filtration or centrifuging, and recovered.

The ZSM-48 produced by the present process generally has the followingmolar composition in its as-synthesized, anhydrous form:(0.01 to <0.1)R²⁺:(0.1 to <0.2)M_(2/n) :xAl₂O₃:SiO₂where R²⁺ is one or more diquaternary ammonium compounds includingMe₆-diquat-5, M is at least one alkali or alkali metal cation of valencen, especially sodium, and x is greater than 0.01, typically greater than0.0125, such as about 0.013 to about 0.02.

In its as-synthesized, anhydrous form, the ZSM-48 produced by thepresent process has an X-ray diffraction pattern including the lines setout in Table 1 below.

TABLE 1 d (Å) Relative Intensity (I/Io) 11.8 ± 0.2  W-VS 10.2 ± 0.2  W-M7.2 ± 0.15 W 4.2 ± 0.08 VS 3.9 ± 0.08 VS 3.6 ± 0.08 W 3.1 ± 0.08 W 2.85± 0.08  W

These values were determined by standard techniques. The radiation wasthe K-alpha doublet of copper, and a diffractometer equipped with ascintillation counter with a strip chart pen record was used. The peakheights, intensity (I), and the positions as function of 2 times theta,where theta is the Bragg angle, were read from the spectrometer chart.From these, the relative intensities, 100 I/Io, where Io is theintensity of the strongest line or peak, and d (obs.), the interplanarspacing in Å, corresponding to the recorded lines, were calculated. InTable 1 the relative intensities are given in terms of the symbols W forweak, VS for very strong and W-S for weak-to-strong (depending on thecationic form). Ion exchange of the sodium ion with cations revealssubstantially the same pattern with some minor shifts in interplanarspacing and variations in relative intensity. Other minor variations canoccur depending on the silicon to aluminum ratio of the particularsample, as well as if it has been subjected to thermal treatment.

The ZSM-48 product of the present process generally contains water fromthe reaction mixture and so normally requires at least partialdehydration before being used as, for example, a catalyst. Dehydrationis generally achieved by heating the as-synthesized product to atemperature in the range of from about 100° C. to about 600° C. in anatmosphere, such as air, nitrogen, etc. and at atmospheric pressure frombetween about 1 and about 48 hours. Dehydration can also be performed atroom temperature merely by placing the ZSM-48 in a vacuum, but a longertime is required to obtain a sufficient amount of dehydration.

The as-synthesized ZSM-48 product also contains the or each diquaternaryammonium compound used as the directing agent in it synthesis and hence,prior to use, the product is normally activated by removal of theorganic material, leaving active catalytic sites within the microporouschannels of the molecular sieve open for contact with a feedstock. Theactivation process is typically accomplished by heating theas-synthesized ZSM-48 product at a temperature of from about 200° C. toabout 800° C., normally in the presence of an oxygen-containing gas.

Where the ZSM-48 produced by the present process is to be used as acatalyst, it may be desirable to combine the ZSM-48 with anothermaterial resistant to the temperatures and other conditions employed inorganic conversion processes. Such materials include catalyticallyactive and inactive materials and synthetic or naturally occurringzeolites as well as inorganic materials such as clays, silica and/ormetal oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Use of a catalytically active material in conjunction withthe ZSM-48 produced by the present may improve the conversion and/orselectivity of the catalyst in certain organic conversion processes.Inactive materials suitably serve as diluents to control the amount ofconversion in a given process so that products can be obtainedeconomically and without employing other means for controlling the rateof reaction. These materials may be incorporated intonaturally-occurring clays, e.g., bentonite and kaolin, to improve thecrush strength of the catalyst under commercial operating conditions.Such material, i.e., clays, oxides, etc., function as binders for thecatalyst. It is desirable to provide a catalyst having good crushstrength because in a petroleum refinery the catalyst is often subjectedto rough handling, which tends to break the catalyst down intopowder-like materials, which cause problems in processing. These claybinders have been employed for the purpose of improving the crushstrength of the catalyst.

Naturally-occurring clays which can be composited with the ZSM-48produced by the present process include montmorillonite and kaolinfamilies. These families include subbentonites, and kaolins commonlyknown as Dixie, McNamee, Georgia and Florida clays or others in whichthe main mineral constituent is halloysite, kaolinite, dickite, nacrite,or anauxite. Such clays can be used in the raw state as originally minedor initially subjected to calcination, acid treatment or chemicalmodification. Binders useful for compositing with the ZSM-48 alsoinclude inorganic oxides, notably alumina.

In addition to the foregoing materials, the ZSM-48 produced by thepresent process can be composited with a porous matrix material such assilica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia. The relative proportions of finely dividedZSM-48 and inorganic oxide gel matrix vary widely with the ZSM-48content ranging from about 1 to about 90 percent by weight and moreusually, particularly when the composite is prepared in the form ofbeads, in the range from about 2 to about 70 percent by weight of thecomposite.

The ZSM-48 produced herein can be used as an adsorbent and as a catalystfor a wide variety of organic conversion processes, but in general isintended for use as a hydrocarbon dewaxing catalyst. With such anapplication, it may be desirable employ the ZSM-48 in combination with ametal component capable of providing the catalysts with ahydrogenation-dehydrogenation function. Suitable metal componentsinclude tungsten, vanadium, molybdenum, rhenium, nickel, cobalt,chromium, manganese, or a noble metal such as platinum or palladium.Such component can be exchanged into the composition, impregnatedtherein or physically intimately admixed therewith. Such component canbe impregnated in or onto it such as, for example, by, in the case ofplatinum, treating with a solution containing platinum metal-containingions. Thus, suitable platinum compounds include chloroplatinic acid,platinous chloride and various compounds containing the platinum amminecomplex.

Catalyst containing ZSM-48 produced by the present process areparticularly useful in the dewaxing catalysts of lube oil basestocks.Such feedstocks are wax-containing feeds that boil in the lubricatingoil range, typically having a 10% distillation point greater than 650°F. (343° C.), measured by ASTM D 86 or ASTM D2887. Such feeds may bederived from a number of sources such as oils derived from solventrefining processes such as raffinates, partially solvent dewaxed oils,deasphalted oils, distillates, vacuum gas oils, coker gas oils, slackwaxes, foots oils and the like, and Fischer-Tropsch waxes. Preferredfeeds are slack waxes and Fischer-Tropsch waxes. Slack waxes aretypically derived from hydrocarbon feeds by solvent or propane dewaxing.Slack waxes contain some residual oil and are typically deoiled. Footsoils are derived from deoiled slack waxes. Fischer-Tropsch waxes areprepared by the Fischer-Tropsch synthetic process.

Dewaxing conditions with such lube oil basestocks typically includetemperatures of up to 426° C., such as from about 250° C. to about 400°C., for example from about 275° C. to about 350° C., pressures of fromabout 791 to about 20786 kPa (100 to 3000 psig), such as from about 1480to about 17339 kPa (200 to 2500 psig), liquid hourly space velocitiesfrom about 0.1 to about 10 hr⁻¹, such as from about 0.1 to about 5 hr⁻¹and hydrogen treat gas rates from about 45 to about 1780 m³/m³ (250 to10000 scf/B), such as from about 89 to about 890 m³/m³ (500 to 5000scf/B).

In addition, catalysts containing ZSM-48 produced by the present processcan also be used for hydroisomerization of normal paraffins,particularly when provided with a hydrogenation component, e.g.,platinum. Typically hydroisomerization is carried out at a temperaturefrom about 100° C. to about 400° C., such as about 150° C. to about 300°C., with a liquid hourly space velocity between about 0.01 and about 2hr⁻¹, such as between about 0.25 and about 0.50 hr⁻¹ employing hydrogensuch that the hydrogen to hydrocarbon mole ratio is between about 1:1and about 5:1.

The invention will now be more particularly described with reference tothe following non-limiting Examples.

Example 1 Preparation of High Activity ZSM-48 using Diquat-5 and LowOH⁻/SiO₂ Ratio

A mixture was prepared from 1040 g of water, 45 g of Pentamethoniumdibromide (50% solution), 200 g of Ultrasil silica, 11 g of sodiumaluminate solution (45%), and 36 g of 50% sodium hydroxide solution.Then 5 g of ZSM-48 seeds was added to the mixture. The mixture had thefollowing molar composition:

SiO₂/Al₂O₃ 102 H₂O/SiO₂ 20 OH⁻/SiO₂ 0.17 Na⁺/SiO₂ 0.17 Diquat-5/SiO₂0.02

The mixture was reacted at 320° F. (160° C.) in a 2-liter autoclave withstirring at 350 RPM for 48 hours. The product was filtered, washed withdeionized (DI) water and dried at 250° F. (120° C.). The XRD pattern(see FIG. 1A) of the as-synthesized material showed the typical purephase of ZSM-48 topology. The SEM (see FIG. 1B) of the as-synthesizedmaterial showed that the material was composed of agglomerates ofelongated needle-like crystals. The as-synthesized crystals wereconverted into the hydrogen form by three ion exchanges with ammoniumnitrate solution at room temperature, followed by drying at 250° F.(120° C.) and calcination at 1000° F. (540° C.) for 6 hours. Theresulting ZSM-48 crystals had a SiO₂/Al₂O₃ molar ratio of 90.4, surfacearea of 265 m²/g, and an Alpha value of 69.

Example 2 Comparative Preparation of Medium Activity ZSM-48 usingDiquat-5, Low OH⁻/SiO₂ Ratio and High SiO₂/Al₂O₃

A mixture was prepared from 1100 g of water, 65 g of Pentamethoniumdibromide (50% solution), 228 g of Ultrasil silica, 6 g of sodiumaluminate solution (45%), and 45 g of 50% sodium hydroxide solution. Themixture had the following molar composition:

SiO₂/Al₂O₃ 195 H₂O/SiO₂ 19 OH⁻/SiO₂ 0.17 Na⁺/SiO₂ 0.17 Diquat-5/SiO₂0.027

The mixture was reacted at 320° F. (160° C.) in a 2-liter autoclave withstirring at 350 RPM for 48 hours. The product was filtered, washed withdeionized (DI) water and dried at 250° F. (120° C.). The XRD pattern(see FIG. 2A) of the as-synthesized material showed the typical purephase of ZSM-48 topology. The SEM (see FIG. 2B) of the as-synthesizedmaterial shows that the material was composed of agglomerates offibrous-like crystals. The resulting ZSM-48 as-synthesized crystals hada SiO₂/Al₂O₃ molar ratio of about 170/1.

Example 3 Comparative Preparation of High Activity ZSM-48 using Diquat-5and High OH⁻/SiO₂ Ratio

A mixture was prepared from 360 g of water, 39 g of Pentamethoniumdibromide (50% solution), 35.6 g of Aerosil 130 silica, 6.9 g ofAl(NO₃)₃.xH₂O and 14.4 g of 50% sodium hydroxide solution. Then 5 g ofZSM-48 seeds was added to the mixture. The mixture had the followingmolar composition:

SiO₂/Al₂O₃ 60 H₂O/SiO₂ 40 OH⁻/SiO₂ 0.33 Na⁺/SiO₂ 0.33 Diquat-5/SiO₂ 0.1

The mixture was aged at room temperature with stirring at 100 rpm for 24hours, and then reacted at 320° F. (160° C.) in a 600 ml autoclave withstirring at 100 RPM for 96 hours. The product was filtered, washed withdeionized (DI) water and dried at 250° F. (120° C.). The XRD pattern ofthe as-synthesized material showed the typical phase of ZSM-48 topology.The SEM of the as-synthesized material showed that the material wascomposed of agglomerates of fibrous-like crystals. The resultingas-synthesized ZSM-48 crystals had a SiO₂/Al₂O₃ molar ratio of ˜52/1.

Example 4 Preparation of High Activity ZSM-48 using Diquat-5 at LowOH⁻/SiO₂ Ratio

A mixture was prepared from 1195 g of water, 69 g of Pentamethoniumdibromide (50% solution), 228 g of Aerosil 200 silica, 22.2 g of 45%sodium aluminate and 41 g of 50% sodium hydroxide solution, and 1.3 g of47% H₂SO₄ solution. Then 10 g of ZSM-48 seeds was added to the mixture.The mixture had the following molar composition:

SiO₂/Al₂O₃ 62 H₂O/SiO₂ 21 OH⁻/SiO₂ 0.18 Na⁺/SiO₂ 0.18 Diquat-5/SiO₂ 0.03

The mixture was reacted at 320° F. (160° C.) in a 2-liter ml autoclavewith stirring at 250 RPM for 96 hours. The product was filtered, washedwith deionized (DI) water and dried at 250° F. (120° C.). The XRDpattern (see FIG. 3A) of the as-synthesized material showed the typicalphase of ZSM-48 topology. The SEM (see FIG. 3B) of the as-synthesizedmaterial showed that the material was composed of agglomerates ofelongated needle or fibrous-like crystals. The as-synthesized crystalswere converted into the hydrogen form by three ion exchanges withammonium nitrate solution at room temperature, followed by drying at250° F. (120° C.) and calcination at 1000° F. (540° C.) for 6 hours. Theresulting ZSM-48 crystals had a SiO₂/Al₂O₃ molar ratio of about 60, anAlpha value of 120 and surface area of 325 m²/g, and n-hexane sorptionof 42.1 mg/g.

Example 5 Preparation of High Activity ZSM-48 using Mixture Diquat-5 andDiquat-6 (Diquat-5/Diquat-6 Molar Ratio of 2.8)

A mixture was prepared from 1200 g of water, 17 g of Hexamethoniumdichloride (56% solution), 60 g of Pentamethonium dibromide (50%solution), 228 g of Ultrasil silica, 16 g of sodium aluminate solution(45%), and 40 g of 50% sodium hydroxide solution. Then 10 g of ZSM-48seeds was added to the mixture. The mixture had the following molarcomposition:

SiO₂/Al₂O₃ 81 H₂O/SiO₂ 20 OH⁻/SiO₂ 0.17 Na⁺/SiO₂ 0.17 Diquat-5/SiO₂0.025 Diquat-6/SiO₂ 0.009

The mixture was reacted at 320° F. (160° C.) in a 2-liter autoclave withstirring at 350 RPM for 48 hours. The product was filtered, washed withdeionized (DI) water and dried at 250° F. (120° C.). The XRD pattern(FIG. 4A) of the as-synthesized material showed the product to be ofZSM-48 topology with a trace of ZSM-50 impurity. The SEM (FIG. 4B) ofthe as-synthesized material showed that the material was composed ofagglomerates of elongated needle-like/fibrous-like crystals. Theas-synthesized crystals were converted into the hydrogen form by threeion exchanges with ammonium nitrate solution at room temperature,followed by drying at 250° F. (120° C.) and calcination at 1000° F.(540° C.) for 6 hours. The resulting ZSM-48 crystals had a SiO₂/Al₂O₃molar ratio of 74.2, an Alpha value of 57 at Na=960 ppm, surface area of222 m²/g, and n-hexane sorption of 33.4 mg/g.

Example 6 Preparation of High Activity ZSM-48 using Mixture Diquat-5 andDiquat-6 (Diquat-5/Diquat-6 Molar Ratio of 1

A mixture was prepared from 1200 g of water, 17 g of Hexamethoniumdichloride (56% solution), 23 g of Pentamethonium dibromide (50%solution), 228 g of Ultrasil silica, 16 g of sodium aluminate solution(45%), 1.3 g of 98% H₂SO₄ solution, and 40 g of 50% sodium hydroxidesolution. Then 10 g of HA-ZSM-48 seed (SiO₂/Al₂O₃ about 70/1) was addedto the mixture. The mixture had the following molar composition:

SiO₂/Al₂O₃ 81 H₂O/SiO₂ 20 OH⁻/SiO₂ 0.17 Na⁺/SiO₂ 0.17 Diquat-5/SiO₂ 0.01Diquat-6/SiO₂ 0.01

The mixture was reacted at 320° F. (160° C.) in a 2-liter autoclave withstirring at 350 RPM for 48 hours. The product was filtered, washed withdeionized (DI) water and dried at 250° F. (120° C.). The XRD pattern(FIG. 5A) of the as-synthesized material showed the typical pure phaseof ZSM-48 topology. The SEM (FIG. 5B) of the as-synthesized materialshowed that the material was composed of agglomerates of elongatedneedle-like crystals with a smaller ratio of L/D (crystalslength/diameter) as compared to Example 5. The as-synthesized crystalswere converted into the hydrogen form by three ion exchanges withammonium nitrate solution at room temperature, followed by drying at250° F. (120° C.) and calcination at 1000° F. (540° C.) for 6 hours. Theresulting ZSM-48 crystals had a SiO₂/Al₂O₃ molar ratio of about 71, anAlpha value of 110, surface area of 281 m²/g, n-hexane sorption of 42.1mg/g.

Example 7 Preparation of Catalyst for N-Decane Testing

A mixture was prepared by combining the H-form ZSM-48 crystals fromExample 4 with alumina. The powders were mixed together using a mortarand pestle followed by pelletizing and sizing to 14/24 mesh. Thismaterial was then dried at 250° F. (120° C.) and calcined at 1000° F.(540° C.) in full air for 6 hours. The calcined material was thenimpregnated with platinum via incipient wetness usingtetraammineplatinum nitrate followed by drying at 250° F. (120° C.) andcalcination in full air at 680° F. (360° C.) for 3 hours. Hydrogenchemisorption (platinum dispersion) data on this material gave 83%dispersion.

Example 8 N-decane Testing

The catalyst from Example 7 was evaluated in an atmospheric n-decaneisomerization unit. Approximately 1 gram of the 14/24 mesh-sizedcatalyst was used for the test. The sample was first heated undernitrogen to 500° F. (260° C.), and then the flow was switched tohydrogen. Hydrogen and n-decane were flowed through the reactor whilethe system cooled to the first setpoint of 325° F. (163° C.). Afterlining out at this temperature, an on-line gas chromatograph analyzedthe product exiting the isomerization unit, until the next set-pointtemperature was attained. The catalyst was evaluated at a total of 9different temperatures within the range of 325° F. (163° C.) to 495° F.(257° C.). The data was retrieved and analyzed. The results are shown inFIGS. 6A and 6B, from which it will be seen that at 400° F. (204° C.)almost 80% of the n-decane has been converted (FIG. 6A) and theselectivity to iso-decane is 50-60% (FIG. 6B).

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein. For this reason, then, reference shouldbe made solely to the appended claims for purposes of determining thetrue scope of the present invention.

1. A process for producing ZSM-48, the process comprising: (a) providingan aqueous reaction mixture comprising at least one source of silica, atleast one source of alumina, at least one source of hydroxyl ions, atleast one source of diquaternary alkylammonium, R²⁺, ions having theformula:(CH₃)₃N⁺(CH₂)₅N⁺(CH₃)₃ and optionally seed crystals, wherein saidreaction mixture has a composition including the following molar ratios:R²⁺:SiO₂ from about 0.01 to about 0.05 SiO₂:Al₂O₃ from about 50 to lessthan 100 OH:SiO₂ from about 0.1 to about 0.2; and (b) crystallizing saidreaction mixture under conditions effective to produce said ZSM-48. 2.The process of claim 1 wherein said reaction mixture has an H₂O: SiO₂molar ratio less than
 30. 3. The process of claim 1 wherein saidreaction mixture also comprises a source of sodium cations and has aNa⁺:SiO₂ molar ratio less than 0.2.
 4. The process of claim 1 whereinsaid reaction mixture also comprises a source of further diquaternaryalkylammonium ions having the formula (CH₃)₃N⁺(CH₂)_(n)N⁺(CH₃)₃ where nis 3, 4, 6, 7, 8 , 9 or
 10. 5. The process of claim 4, wherein saidreaction mixture also comprises a source of further diquaternaryalkylammonium ions having the formula (CH₃)₃N⁺(CH₂)₆N⁺(CH₃)₃.
 6. Theprocess of claim 5 wherein the molar ratio of total diquaternaryalkylammonium ions to SiO₂ in the reaction mixture is less than 0.1. 7.The process of claim 1 wherein said conditions in (b) include atemperature of about 120° C. to about 200° C. for a time of about 12 toabout 200 hours.
 8. The process of claim 1 wherein the reaction mixturecomprises ZSM-48 seed crystals.
 9. The process of claim 8 wherein theZSM-48 seed crystals are present in an amount between about 50 ppm byweight to about 50,000 ppm by weight of the reaction mixture.
 10. Amethod for dewaxing a hydrocarbon feedstock, comprising contacting thehydrocarbon feedstock under dewaxing conditions with ZSM-48 prepared bythe process of claim 1 where the ZSM-48 material is furthercharacterized as having both fibrous and needle crystalline morphology.11. A process for producing ZSM-48, the process comprising crystallizinga an aqueous reaction mixture comprising at least one source of silica,at least one source of alumina, at least one source of hydroxyl ions, atleast one source of first diquaternary alkylammonium ions having theformula:(CH₃)₃N⁺(CH₂)₅N⁺(CH₃)₃ at least one source of second diquaternaryalkylammonium ions having the formula:(CH₃)₃N⁺(CH₂)_(n)N⁺(CH₃)₃ where n is 3, 4, 6, 7, 8 , 9 or 10, andoptionally seed crystals.
 12. The process of claim 9 wherein said seconddiquaternary alkylammonium ions are (CH₃)₃N^(+(CH) ₂)₆N+(CH₃)₃.
 13. Theprocess of claim 9 wherein said reaction mixture has a SiO₂:Al₂O₃ molarratio less than
 100. 14. The process of claim 9 wherein the molar ratioof the sum of the first diquaternary alkylammonium ions and the seconddiquaternary alkylammonium ions to SiO₂ in the reaction mixture is lessthan 0.1.
 15. The process of claim 9 wherein the reaction mixturecomprises ZSM-48 seed crystals.
 16. The process of claim 15 wherein theZSM-48 seed crystals are present in an amount between about 50 ppm byweight to about 50,000 ppm by weight of the reaction mixture.
 17. Theprocess of claim 9 wherein said crystallizing conditions include atemperature of about 120° C. to about 200° C. for a time of about 12 toabout 200 hours.
 18. A method for dewaxing a hydrocarbon feedstock,comprising contacting the hydrocarbon feedstock under dewaxingconditions with ZSM-48 prepared by the process of claim 11 where theZSM-48 material is further characterized as having both fibrous andneedle crystalline morphology.